2-2 Average root, shoot, and total dry weight per seedling
after outplanting compared to seedlings remaining
in the nursery................ ........................ 57

2-3 Root and shoot moisture content of outplanted seedlings as
compared to those remaining in the nursery............. 59

2-4 Average dry weight of new roots per seedling after
outplanting............................................ 61

2-5 Average sugar and starch concentration per seedling after
outplanting, compared to those of seedlings remaining in
the nursery............................................ 67

2-6 Average root starch concentration after outplanting com-
pared to that of seedlings remaining in the
nursery................................................ 68

2-7 Average carbohydrate concentrations and absolute amounts
for whole seedlings after outplanting compared to those of
seedlings remaining in the nursery..................... 70

2-8 The regression of survival at 1 year over the number of
undercutting prior to outplanting .................... 72

2-9 The regression of first year height growth over the number
of undercutting prior to outplanting.................. 73

2-10 Relationship of survival at 1 year after outplanting to
average mass of new roots per seedling during the first 12
weeks after outplanting ............................ 76

2-11 Relationship of average new root mass per seedling during
the 2-12 week period after outplanting to total non-
structural carbohydrate concentration during the same
period................................................. 77

Figure 2-2. Average root, shoot, and total dry weight per seedling after
outplanting compared to seedlings remaining in the nursery. Values for
nursery seedlings were given in Chapter I. Bars indicate + S- Shaded
Sx
bars in the bottom indicate rainfall at the planting site for specific
dates.

4 TOTAL

SHOOT

Outplanted

ROOT

I--I I
t---i-- i-- ^

Rainfall

II 1 1

2 4 6 8

WEEKS AFTER PLANTING

Nursery

-O---o-

(Jan 6)

(Mar 31)

Figure 2-3.
compared to
for nursery

Root and shoot moisture content of outplanted seedlings as
those remaining in the nursery. Bars indicate + S-. Values
seedlings were presented in Chapter I.

SHOOTS

Nursery o-o
Outplanted *-*

ROOTS

-KI

Nurseryo-o
Outplanted -- *

WEEKS AFTER OUTPLANTING

240,

200 L

160

120

240

0 2 4 6 8 10

12

(Mar 31)

I I

(Jan 6)

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a-- a Control I
S50 -* 1
AA- 2

I
E2 40

UJ /
30

S1Q

01 T I I

0 2 4 6 8 10 12

(Jan 6) WEEKS AFTER PLANTING (Mar 31)

Figure 2-4. Average dry weight of new roots per seedling after outplanting.
Bars indicate the largest S- for any one sample date.

The only treatment x time interaction concerned new root

production. Treatment 2 and 3 added new roots faster and earlier

than either treatment 1 or the control (Figure 2-4). The growth

of new roots began after four weeks in the field. This is im-

mediately before the surge in total dry weight occurring after 6

weeks (Figure 2-2). Also, new root growth occurred even while the

overall root moisture content declined (Figure 2-3).

Changes in Carbohydrate Reserves after Planting

Analysis revealed no interaction between time and treatment

for any carbohydrate variable, either concentrations or amounts.

This allowed comparison among times using combined treatment

averages and comparisons among treatments using combined time

averages.

Although mean total carbohydrate content differed apprec-

iably with treatment, only one of the differences in carbohydrate

concentration or content was statistically significant (Table

2-5). This may be a result of the relatively small sampling unit

(five seedlings) or the relatively variable field environment.

Only root starch mass was found to vary significantly by treat-

ment. This relationship was linear, with amounts of root starch

increasing with intensity of nursery undercutting.

Carbohydrate reserves changed significantly with sampling

date (Table 2-6). From January 20 (2 weeks after planting) to

March 31 (12 weeks after planting), sugar concentrations

r-

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decreased while starch concentrations increased. The only excep-

tion to this trend was shoot sugar concentrations which increased

from the second to fourth week after outplanting (January 20 to

February 3), then began to decline.

The values determined for root and shoot starch concentra-

tions at time zero are unreliable due to sample thawing after a

freezer malfunction. These values are shown in Table 2-6, how-

ever, because they are similar to those of nursery samples taken

near the same time (Figure 2-6). If they are accurate, they

would indicate a 44% decrease in root starch concentrations dur-

ing the first 2 weeks after outplanting.

The changes over time in carbohydrate concentrations after

outplanting were remarkably similar to the changes in nursery

seedlings during the same period (Figure 2-5, 2-6, 2-7). Starch

concentration increased and sugar concentration decreased in

both. Generally, reserve concentrations of outplanted seedlings

followed the same seasonal trends as were encountered in seed-

lings remaining in the nursery.

There were, however, two important differences between the

data sets. First, starch concentrations of outplanted seedlings

were lower than those of nursery seedlings during the first 8

weeks, whereas sugar concentrations were higher (Figure 2-5).

Figure 2-5. Average sugar and starch concentration per seedling after
outplanting, compared to those of seedlings remaining in the nursery.
Bars represent + S- Values for nursery seedlings were presented in
Chapter I; lines here have been extended to values for December 28.
The value for starch concentration of Time 0 is actual analysis result,
but may be erroneous (see text).

~

Nursery o0-

Outplanted *- *

STARCH

I I

WEEKS AFTER OUTPLANTING

SUGARS

100

90

80

70

60

50

100

80

(Jan 6)

(Mar 31)

0) -
S- 4-)
L C
0 0
O *

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is., -
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ii

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0 E
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S0
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L.L. *r- tn *r-

I I

Figure 2-7. Average carbohydrate concentrations and absolute amounts
for whole seedlings after outplanting compared to those of seedlings re-
maining in the nursery. Bars represent + S- Values for nursery sam-
x
ples were presented in Chapter I; lines here have been extended to
values for December 28.

4. Increment = .28 (x) + 5.5 R2 = .31
where increment is the first year's height growth,
and x = average mg of new roots per seedling 2-12 weeks
after outplanting.

5. New Roots = .43 (x) 35 R2 = .50
where new roots = average mg of new roots per seedling
2-12 weeks after outplanting
and x = average total carbohydrate concentration per
seedling 2-12 weeks after outplanting.

100

90

Z 80

0 0

y = 1.lx + 61.2

60 r

NEW ROOTS mg/seedling dry wt

Figure 2-10. The relationship of survival at 1 year after outplanting to
average mass of new roots per seedling during the first 12 weeks after
outplanting. Each point is an average of 24 composite samples of five
seedlings and includes six sampling dates.

o\ *

O- )

II II

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Discussion

The lack of morphological variation between treatments at

the time of lifting was due to two factors: (1) the treatments

were applied in November-December when top growth had slowed

(Chapter I); and (2) the 8 week time lapse was not sufficient

enough for statistically significant differences to develop.

Studies that have found significant morphological variation due

to undercutting involved actively growing seedlings and treat-

ments applied over a several month period (Rook 1971, Tanaka et

al. 1976). In fact, radiata pine seedlings must be root wrenched

when they are actively growing to achieve the desired morpholo-

gical and physiological modifications (Rook 1971).

Root dry weight was unaffected by the intensity of root

pruning (Table 2-2), which concurs with studies of radiata pine

(Rook 1971) and loblolly pine (Tanaka et al. 1976). In the

present study, the form of roots was modified rather than total

weight. November and December is a period when seedlings were

actively adding root weight (Chapter I). In undercut seedlings

this increase occurred on 70% of the original root mass, inasmuch

as 30% had been lost at the first undercutting (Figure 2-2).

The more intensive root pruning treatment distributed this in-

crease among a larger number of new roots (Table 2-2). The

result of the various undercutting intensities was to produce

seedlings of similar dry weight but different root morphologies.

Nursery root pruning caused a profusion of new roots. Root

auxin and cytokinin activity are increased by root pruning (Carl-

son and Larson 1977). It is the specific balance of these two

hormones that controls root primordia initiation (Altman and

Wareing 1975). Undercutting produced more new roots and root

primordia which could expand upon outplanting. The effect of

nursery undercutting continued in the field where intensively

undercut seedlings produced new roots faster and in greater quan-

tities than controls (Figure 2-4).

Morphological and physiological development after outplant-

ing closely followed that of undisturbed seedlings in the nur-

sery. Apparently, the degree of "transplant shock" experienced

by the seedlings in this experiment was not great. The results

clearly show that growth can begin shortly after planting. The

large dry weight increases between the fourth and sixth week

after planting (Figure 2-2) indicate that photosyntehtic capacity

must have been restored. In fact, increases in TNC indicate that

net photosynthesis began soon after the second week in the field.

There was only 2.5 mm of rainfall during the first 2 weeks after

planting. The increase in TNC after 2 weeks in the field

coincided with several good rains (Figure 2-7).

Caution is adviseable when interpreting results from a sin-

gle year study. Lower rainfall or antecedent soil moisture might

have limited the ability of seedlings to re-initiate carbon as-

similation. Furthermore, lower soil temperature might well have

slowed root expansion (Nambiar 1979).

The seedlings did not put out roots at the expense of

shoots. Both roots and shoots added dry weight at the same rate

they would have in the nursery. One might expect the plant to

direct photoassimilates to restore root systems damaged as a re-

sult of the lifting and planting process. It has been shown that

undercut seedlings may translocate a larger proportion of photo-

assimilated 140C to their roots than untreated controls (Rook

1971, Bacon and Bachelard 1978). Such redirection to roots did

not occur after outplanting in the present study. In fact, when

dry weight of outplanted seedlings equaled that of nursery seed-

lings at about 8 weeks after planting, it was due to the large

increases in shoot mass, inasmuch as root mass was still less

than that of nursery seedlings (Figure 2-2). During the 12 week

period of this study, root dry weight increased by 0.39 g, while

shoot dry weight increased by 0.70 g (Table 2-3).

The results of this study concur with the hypothesis that

root growth potential is a good indicator of field performance

(Sutton 1980) and is a better indicator than the morphological

characteristics generally used for grading seedlings. The amount

of new roots found on seedlings during the 2 to 12 week period

after outplanting correlated with both survival and height incre-

ment (Table 2-7). No morphological variable, including root/-

shoot ratio, showed any correlation with performance.

A certain amount of the unaccounted variability in the

regression of first year height increment and new roots (R =

.48), is a result of site conditions. The experimental area

covered 0.17 ha (.44 ac) and subjected seedlings to a range of

microsites, arising from varying degrees of vegetative com-

petition, logging debris, and water retention. Furthermore, the

soil is sandy and well-drained. Bedding was a result of standard

operating procedure rather than a site specific recommendation.

Bedding dry sites may in fact decrease first year height incre-

ment (Broerman et al. 1981). Water stress, especially during the

late summer, could have caused the relatively small seedling

height increment during the first year.

It cannot be concluded from this study that RGP is dependent

upon carbohydrate reserves. Although the amount of new roots was

positively correlated to the total carbohydrate concentrations

averaged over the 2 to 12 week period after outplanting (Figure

2-11), this is not to say that one causes the other.

There was no indication that carbohydrate reserves were used

to support root or shoot growth for more than a very brief period

after planting. Although TNC decreased during the first two

weeks after planting, it increased thereafter. The seedling re-

established its normal wintertime pattern of carbohydrate ac-

cumulation (Figure 1-9) before substantial growth occurred. As

outplanted seedlings caught up and then surpassed nursery

seedlings in total dry weight, they also surpassed them in total

reserves. The uncrowded, sunny conditions of field planting ap-

parently became beneficial after an initial phase of reduced dry

weight accumulation. Seedlings remaining in the nursery at a

density of approximately 30 per square foot were individually

exposed to less light and intense competition for soil moisture

and nutrients.

The decline in TNC in the first few weeks after planting was

relatively small, from 370 mg of non-structural carbohydrate at

the time of lifting (based on Chapter I results) to 317 mg after

2 weeks, a decline of only 15%. Moreover, part of the decrease

is due to the loss of 30% of seedling root mass and its included

reserves during lifting and outplanting. Nevertheless, an im-

portant part of the decline must have been due to utilization by

the seedling, as is evidenced by a 19% decrease in TNC concen-

trations (Figure 2-7).

The loss of carbohydrate concentration involved only the

starch fraction, specifically root starch. The simultaneous

increase in seedling sugar concentrations indicates that starch

was being transformed to sugar (Figure 2-5). The reason for the

increase in sugar concentrations is unclear.

The transformation of starch to sugar may be related to the

internal water balance of the seedling. Water loss or drought is

generally regarded as the most serious cause of seedling mor-

tality (Wakeley 1954, Kozlowski 1979). A substantial part of the

absorbing root surface is lost during lifting. Storage, trans-

port, and planting may further desiccate roots. Hence, control

of subsequent water loss is essential for seedling survival.

During the first 8 weeks after outplanting, the moisture content

of seedlings declined (Figure 2-3). The simultaneous increase in

sugar concentrations suggested the possibility of free sugars as

osmoregulators to check water loss and maintain a positive turgor

potential. The role of free sugars as osmoregulators has been

discussed by Hsiao et al. (1976) and Turner and Jones (1980).

A capacity for osmotic adjustment would be highly advanta-

geous for outplanted seedlings. By lowering cell osmotic

potential, turgor and turgor-dependent processes can be main-

tained. The result is continued cell enlargement and growth,

open stomata, and photosynthesis at water potentials which would

otherwise by limiting (Kramer 1983). As noted previously, net

photosynthesis presumably began between the second and fourth

week after outplanting in a period when the seedlings were still

losing water.

The results suggest the sequence of events after outplanting

to be: (1) an immediate transformation of starch to sugars used

for respiration, metabolism, and possibly osmoregulation; (2) re-

initiation of photosynthesis when the internal moisture condition

is favorable; (3) re-establishment of the normal seasonal carbo-

hydrate accumulaton; (4) expansion of new roots from existing

root tips and meristems in various stages of development, both

more abundant in seedlings previously root pruned; and (5) shoot

expansion. The critical role of carbohydrate reserves is during

the first step when an unfavorable water balance prohibits photo-

synthesis. By their osmoregulatory ability, carbohydrates can

contribute to a favorable internal water potential. The extent

of this contribution would depend upon the severity and extent of

water deficits.

Nursery undercutting improved seedling performance by

affecting one or more of these steps. Upon undercutting, a large

portion of the seedling root absorption system is lost. The re-

sulting water deficits would initiate the conversion of starch to

sugar for the osmoregulatory process. Repeated undercutting

could result in stable high cell osmotic potentials. These seed-

lings would be more resistent to water loss when outplanted. A

second effect is the increased number of root tips and more fi-

brous root system of undercut seedlings. This would facilitate

water uptake after planting (Rook 1971, Tanaka et al. 1976, Bacon

and Bachelard 1978). Nursery undercutting therefore has the po-

tential to increase seedling performance by increasing water ab-

sorbing surface area, and by changing seedling physiology so as

to decrease water loss due to desiccation.

CHAPTER III
THE EFFECT OF WATER STRESS ON SEEDLING MORPHOLOGY
AND CARBOHYDRATE PHYSIOLOGY